Pneumatic process for tube processing



Oct. 25, 1966 ESKIJIAN PNEUMATIC PROCESS FOR TUBE PROCESSING Filed Sept. 9, 1965 IN VENTOR.

LUTHER ESKIJ IAN United States Patent 3,280,845 PNEUMATIC PROCESS FOR TUBE PROCESSING Luther Eskijian, Altadena, Calif. Specialties Engineering Corp., 340 Washington Blvd., Pasadena, Calif.) Filed Sept. 9, 1965, Ser. No. 486,072 9 Claims. (Cl. 13897) This invention relates to a method and apparatus for processing the interior of tubes in which pneumatic pressure is employed.

A coating upon the interior wall of a tube is frequently required in order that it be protected to serve for an extended period if the tube is new, or to resurface or repair the tube if it has become defective in use. Illustrative of the second kind of processing is the coating of cooling condenser tubes in situ. Such tubes are invariably disposed horizontally and a problem arises in insuring a coating at the top of the inner wall of the tube because of the effect of gravity.

I have found that by employing air pressure to force a viscous material past a plunger the effect of gravity is overcome. Additionally, a greater air pressure may be employed to drive the plunger through the tube. By suitably selecting the process it is possible to repair badly corroded tubes having holes in the walls, to coat over pits and corroded areas with a smooth coating, or to coat new tubes. According to thi invention the process is relatively quickly accomplished, as is necessary when using certain preferred viscous materials and is desired when a great number of tubes are to be processed.

An object of this invention is to provide a pneumatic process for coating the interior of tubes.

Another object is to repair corroded tubes.

Another object is to process the interior of tubes rapidly, at relatively low cost and with relatively simple apparatus.

Other objects will become apparent upon reading the following specification and upon examining the accompanying drawings, in which are set forth by way of illustration and example certain embodiments of this invention.

FIG. 1 is a longitudinal section illustrating one method and means for repairing a horizontally disposed tube,

. FIG. 2 is an end elevation of the same, and

FIG. 3 is a longitudinal section illustrating another related method and apparatus for coating a tube; the pneumatic fittings being shown schematically.

In FIG. 1, numeral 1 indicates a tube or the like that is to be coated internally or repaired by filling pits and/ or plugging holes in the interior surface thereof. The tube may be of any size, shape and may be fabricated of substantially any material, but typically it is a hollow cylindrical tube of a condenser or heat exchanger, fabricated of copper, brass, bronze, monel metal or stainless steel. A typical diameter is in the range of /2 to 1 inch and the length may be up to 50 feet.

A fragmentary showing of a tube sheet 2 at the first (left-hand) end of tube 1 is typical of an installation of tubes in a condenser, there being numerous other tubes above, below, behind and in front of the illustrative tube shown. Normally, the cooling fluid; which may be sea water, river water or lake water, or water recirculated in a closed captive system; flows through tube 1 and the steam or other working substance to be condensed flows around the outside of the tube. A second tube sheet 3 3,280,845 Patented Oct. 25, 1966 "ice supports tube 1 at the right-hand end thereof, the juncture being liquid tight. Tube 1 has been shown broken at the center in order that the scale of the drawing will show the desired detail at the ends.

Before tubes are processed according to this invention the same are preferably cleaned by passing known cleaning brushes, etc. through the same, and/or by employing known cleaning chemical means.

In accomplishing the subject process according to FIG. 1, pull cable 4 is first pushed through the length of the tube. This cable may be a stranded bronze fishing line having a number of strands of the order of & inch, being capable of sustaining a pull of several hundred pounds. An equivalent known plastic woven rope cord may also be used. Spreader plunger 6 is then attached to the cable and allowed to hang down at the left end of tube 1 so that material 5 may be inserted.

An alternate and preferred manner of passing cable 4 through tube 1 consists of retaining plunger 6 fastened to cord 4 at all times and traversing the plunger and the cable from the right-hand end to the left-hand end of the tube by pneumatic means, as by compressed air introduced at the right-hand end of the tube after the plunger and the starting end of the cable have been placed therein.

In any event, plunger 6 is allowed to hang down at the left-hand end of tube 1 and material 5 is introduced at this first end of the tube, as with the aid of a caulking gun or an equivalent means.

Material 5 is of the general class used for caulking purposes. A particularly suitable material is an epoxy resin. Thistype of material consists of two components which are mixed just prior to use. The resulting combination hardens within a relatively short time; this interval being known as the pot life. It is for this reason that rapid processing according to this invention is desirable, if not absolutely necessary.

For optimum results a particular viscosity for the material is desirable, such as honey on a cold day, say at 60 F. That is, the material is more plastic than liquid. This is preferable so that the material will suitably coact with the air pressure and/or the forces brought into play according to this invention, while also being fluid enough to extend circumferentially all around the means employed to spread it within the tube and thus to completely coat the interior thereof.

A suitable material available to the trade is manufactured by the Specialties Engineering Corporation of Pasadena, California, and is known as Specoat, SEC- ETA modified CL. Their SEC-ETP material may also be used. The letters specifying the material have the following significance; SEC, initials of the corporation; E, epoxy; T, trowelable; A, adhesive; C, caulking; L, lightweight; P, pigmented.

It has been found that a proper criterion for the consistency of the viscous material is that it form an interface with air under pressure that is substantially perpendicu lar to the axis of the tube as the process is being carried out. This is shown at the right-hand side of the material 5 in FIGS. 1 and 2. This meets the requirement that the material stay in place until the chemical reaction taking place between the two components of the epoxy harden it sufiiciently to make it stay in place. This phase of the reaction takes place about half way during 3 the interval between the mixing of the components and the completion of the chemical process.

The so-called pot life of an epoxy material is the period of time during which it is workable. After this period it has hardened, or set, to such a degree that it can no longer be manipulated for any use to which it might be put. The pot life depends upon several factors and these should be given attention in carrying out processing according to this invention. The pot life of the materials specified above is approximately 15 minutes at 72 F., but only minutes at 100 F. If the material is confined, as in the processing step proper herein, the pot life is only about 3 minutes. Thus, a rapid process ing arrangement, as provided by this invention, is required.

The weight of material to be injected into the tube depends upon the diameter and the length of the tube. For an average used tube the amount of material required for coating is 6 grams per lineal foot. Thus, for a 50 foot long tube the total amount is 300 grams. The amount of material required also depends upon the diameter of the tube and the amount of cavitation and erosion, or corrosion, present. More material is required when these use factors are severe.

In the process according to FIG. 1, provision must be made for the escape of the confined air as the spreader plunger 6 decreases the volume of the same during its right-ward traverse of the tube. If there are one or more holes in the tube, as may have been caused by corrosion in prior operation, the escape of air may be approximately correct during the processing. The exact pressure is not critical, but it is found that the force required upon pull cable 4 becomes more than can be conveniently exerted if air is not exhausted by one means or another. In the simple embodiment shown in FIG. 1, air may be exhausted by suitable finger pressure upon valve to open this valve as required to maintain a proper working pressure. Stopper 7 should be resilient and should be strongly urged into tube 1 so that it will not blow out during processing.

Turning to the details of the elements employed for processing, plunger 6 may be made of a section of Teflon rod. The outer diameter of the plunger is related to the inner diameter of the tube such that a suitable coating is deposited upon the tube. For a tube of A" inside diameter the diameter of plunger 6 is 0.004" to 0.006" smaller than the inside diameter of the tube. The front (right-hand) end of this spreader plunger 6 is formed into a rounded frustrum of a cone. This shape properly flows viscous material 5 toward the periphery of the plunger such that it uniformly coats the inner surface of the tube.

As has been intimated, at the second end of tube 1, at tube sheet 3, means to close the tube and to admit and/or exhaust compressed air, such as stopper 7, is employed. This stopper is provided with a slot 8, of small cross-section, in an axial direction at one point around the periphery, through which pull cable 4 is threaded. The stopper has valve bushing 9, with normally closed valve 10 within the same, in a simple embodiment of the invention. Parts employed for auto tires may be used.

Stopper 7 is preferably inserted by a second operator at the time cable 4 has been completely threaded through the tube, so that minimum time will elapse between the time material 5 is injected and the coating of the tube is completed. When plunger 6 and the cable are moved through the tube together from right to left, stopper 7 and its fitments may be used to supply the pneumatic pressure. This pressure drops to zero when the stopper emerges from the first end of the tube (the left-hand); after which material 5 is inserted into the tube.

In any event, as soon as the configuration shown in FIG. 1 has been formed, a few pounds of air pressure is established within tube 1 from stopper 7 to the front face of material 5. A pressure of from 2 to 5 pounds per square inch is suitable. This may be provided by a hand pump, or by a source of compressed air with a known regulator that is set at a pressure in the range of from 2 to 5 #/sq.". A lower pressure is used when the ambient temperature is low, since the material is more viscous and forms, in effect, its own back pressure.

Promptly after the configuration is formed pull cable 4 is pulled to the right in FIG. 1. This may be accomplished by hand, or by a small power operated winch. The speed of traverse of spreader plunger 6 within the tube should be of the order of one-half foot per second. A suitable range of speeds extends from one-fourth foot per second to two feet per second. If the temperature is high and material 5 has a high viscosity as a result of the high temperature, then the most rapid speed would be in order, and vice versa.

In FIG. 1 a hole 11, caused by corrosion or the like, is shown. A plug 12 of viscous material is also shown within the hole. By employing the material and the technique of this invention, this desirable action takes place. The plug of material hardens in place, neither passing completely through hole 11, nor dropping back into the bore of the tube should the hole be located on the top of the same. When holes are to be filled a rate of traverse at the low end -of the range given is employed to provide time for the passage of the viscous material through the hole.

It will be understood that for exceptionally heavy epoxy materials and under certain conditions of application, such as low temperature, the pressure at stopper 7 is best reduced to zero. However, under such conditions, the amount of the deposit to give a uniform coating cannot be as accurately controlled as when back pressure can be employed.

FIG. 2 illustrates an end view of a tube under processing according to FIG. 1 and the reference numerals have the same meaning as in that figure.

FIG. 3 shows an all-pneumatic alternate method and apparatus, such as is best adapted for coating the interior of new tubing, or for coating used tubing that does not have holes.

In the arrangement of FIG. 3, tube 1, material 5 and spreader plunger 6 are as has been previously described and the latter two elements are introduced initially at the left end of the tube. Stopper 7 is modified to stopper 14 by eliminating slot 8 and it is provided with both an air inlet fitting 15 and exhaust valve 16. The former preferably has valve 17, comprised, for example, of spring 18, ball 19 and seat 20, which elements are positioned in that order from left to right. The spring is proportioned so that air over a certain minimum pressure, say 2 #/sq.", will be admitted, but none will be allowed to exhaust. The air is introduced by pump or continuous air pressure means, as before. Exhaust valve 16 may have the same construction as valve 17, but with the elements in reverse order. Also, spring 21 is stronger than spring 18, so that exhaust will take place at some higher pressure, as 5 #/sq.".

At the left end of tube 1 in FIG. 3, stopper 23 is forced into the tube for the processing. Tubing 24 connects to a continuous supply of air, not shown, and pressure regulator 25, shown diagrammatically, is attached to tubing 24. The pressure regulator is set for a desired pressure in the range of from 10 to #/sq., so that spreader plunger 6 will be forced through tube 1 from left to right. The desired pressure is determined by the operating temperature, the viscosity of the material, the quantity of material and its coetficient of friction within the tube. A high pressure is required for high values of these variables, save for the viscosity, for which the reverse is true. High pressure also tends to result in a greater speed of traverse. The back pressure set by valve 16 provides the pressure to keep material 5 in front of spreader plunger 6, so that it will be dispensed to the inner wall of tube 1, thereby to adhesively coat it. It might be thought that the greater driving pressure behind (to the left of) plunger 6 would act to prevent coating of the'tube by the viscous material. However, the adhesiveness of this material is so great that the thin coating, of the order of 0.003, acts as 'a sealer and does not allow the higher pressure to blow by.

By adding a volume meter 26 of known type in the air input line 24-27 and observing the reading of the same after a calibration run it is possible to observe and thus to regulate the speed of traverse of plunger 6 and also to obtain an indication of the location of this plunger at any time during the processing of the tube along its length. This presupposes operation at constant pressure, or a correction to compensate for variable pressure if such is employed during the traverse of a tube.

Also, should insufiicient material 5 be employed for any coating run, this can be sensed by noting an abnormal increase in pressure on the low pressure (right-hand) side and an abnormally large volume of air passed on the high pressure (left-hand) side. This signifies the leakage of high pressure air past plunger 6 from left to right.

It has been determined that the thickness of the coating of the material deposited upon the inner wall of the tube is less than the difference in radii between the rear cylindrical section of plunger 6 and that of the inner wall. The thickness is determined by the viscosity of the material used, the temperature of the tube and the speed of transmission of plunger 6 through the tube; the latter being governed by the pressures employed.

While the term tube has been employed herein, this is also intended to include the term pipe. Also, the term air infers the substitutional use of other gases; such as nitrogen, helium, or mixtures of gases. The use of other gases may coact properly with substance 5; for example, where the material should not be oxidized air would not be used, but nitrogen or some other relatively inert gas.

In repairing condenser tubes according to the process of this invention it is realized that the heat transfer coefficient of the tubes is reduced, per se. However, since tubes having holes may be placed back in service rather than being blocked-off, as is usual practice, and since the flow of water through treated tubes is increased due to the reduced frictional resistance of the plastic lining as compared to the prior pitted surface, it is found that the efiiciency of the condenser is definitely increased.

Although this invention has been described in its preferred forms with a certain degree of particularity, it is to be understood that this disclosure has been made only by way of example and that various changes in the details of construction and processing, and in size, proportions, combination and arrangement of parts may be made without departing from the spirit and scope of the invention as claimed below.

Having thus fully described my invention and the manner in which it is to be practiced, I claim:

1. The process for repairably coating the interior of a tube which includes the steps of;

(a) inserting a viscous material within the first end of said tube,

(b) inserting only one rigid spreader plunger behind said material within the first end of said tube,

(c) providing a pneumatic force originating at the second end of said tube directly against said viscous material to urge it past said spreader plunger to coat the interior of said tube, and

(d) providing a force greater than said pneumatic force to traverse said spreader plunger from the first to the second ends of said tube.

2. The process for repairing a metallic tube which includes the steps of;

(a) inserting a single pull cable having attached only one rigid spreader plunger within said tube with said spreader plunger outside the first end of said tube,

(b) attaching a stopper having an air control valve at the second end of said tube,

(c) injecting a given amount of viscous material for repairing said tube into said tube near said first end of said tube,

( d) inserting said spreader plunger within said first end of said tube behind said material,

(e) introducing a gas into said tube through said control valve to directly force said material to, around, and beyond said spreader plunger, and

(f) pulling said cable from said first end toward said second end of said tube to coat the interior thereof with said viscous material,

(g) while exhausting said gas to maintain the pressure thereof substantially constant within said tube.

3. The process for repairably coating the interior of a tube according to claim 2 in which said tube has at least one hole in the wall thereof, which includes;

(a) injecting a larger than said given amount of viscous material into said tube, and

(b) pulling said cable more slowly than in claim 2, thereby to exude some of said viscous material through said hole to plug the same in addition to coating the inner wall of said tube.

4. The process for repairably coating the interior surface of a tube which includes the steps of;

(a) inserting viscous material within the first end of said tube,

(b) inserting only one rigid spreader plunger behind said material Within the first end of said tube,

(c) attaching means to the first end of said tube for establishing a first air pressure between said spreader plunger and said first end of said tube,

((1) attaching means to the second end of said tube prior to step (a) for establishing a second air pressure directly between said viscous material and said second end of said tube, and

(e) driving said spreader plunger from said first end to said second end of said tube by maintaining said first air pressure greater than said second air pressure during the traverse of said spreader plunger through said tube.

5. Means for sealant coating the interior wall of a tube comprising;

(a) a single rigid spreader plunger having a rounded tapered front end section and an essentially constant diameter section contiguous therewith,

said constant diameter section being smaller than the internal diameter of said tube,

(b) pneumatic means to provide a force directly upon sealant material in the direction against said tapered front end to urge said sealant material past said spreader plunger from said tapered front end, and

(c) means to cause said spreader plunger to traverse said tube With the tapered section forward against said force to provide a sealant coating upon said interior wall.

6. The means for sealant coating of claim 5 in which;

(a) said means to provide a force comprise a stopper located at the end of said tube initially away from said sealant material and said spreader plunger, and

(b) pneumatic means attached to said stopper to provide an air pressure greater than ambient air pressure within said tube directly between said sealant material and said stopper.

7. The means for sealant coating of claim '5 in which said means to traverse said spreader plunger comprises;

(a) a single pull cable attached to said spreader plunger.

8. The means for sealant coating of claim 5 in which said means to traverse said spreader plunger comprises;

(a) additional pneumatic means attached to the opposite end of said tube from said previously recited pneumatic means,

to provide a force in the direction directly against said constant diameter section of said plunger, and

(b) means connected to said additional pneumatic means to cause said force in the direction directly against said constant diameter section to exceed said force in the direction against said tapered front end of said spreader plunger.

9. The means for sealant coating of claim 5 in Which (a) said force in the direction of said tapered front end for directly urging said sealant material is largely provided by the motion of said spreader plunger as it traverses said tube and the adhesion of said sealant material to said interior Wall of said tube.

References Cited by the Examiner UNITED STATES PATENTS 2,804,147 8/1957 Pistole et al 138-97 X 8 6/1962 Green.

12/1964 Xenis et al. 138-97 References Cited by the Applicant UNITED STATES PATENTS 2/ 1930 Cotton.

10/1957 Br ant.

9/1958 Bernard et a1.

2 0 52 10 1957 Brant 133 97 15 T. MOORHEAD, Assistant Examiner. 

1. THE PROCESS FOR REPAIRABLY COATING THE INTERIOR OF A TUBE WHICH INCLUDES THE STEPS OF; (A) INSERTING A VISCOUS MATERIAL WITHIN THE FIRST END OF SAID TUBE, (B) INSERTING ONLY ONE RIGID SPREADER PLUNGER BEHIND SAID MATERIAL WITHIN THE FIRST END OF SAID TUBE, (C) PROVIDING A PNEUMATIC FORCE ORIGINATING AT THE SECOND END OF SAID TUBE DIRECTLY AGAINST SAID VISCOUS MATERIAL TO URGE IT PAST SAID SPREADER PLUNGER TO COAT THE INTERIOR OF SAID TUBE, AND (D) PROVIDING A FORCE GREATER THAN SAID PNEUMATIC FORCEE TO TRAVERSE SAID SPREADER PLUNGER FROM THE FIRST TO THE SECOND ENDS OF SAID TUBE. 